What is a prt?
A portal (.prt) file is a list of the portals in your .BSP, generated by VBSP and then used by WIS to perform visibility calculations.
1. If you run the mod and you get a error saying - "ERROR Prt was not built would you like to continue?"
2. Find any Leaks or Holes in your map.
3. If it still says that. Find any func_door parts that lead to the void. and block it with blocks
4. Rerun the Mod
5. then it works!